Preservatives - refers to substances that can inhibit the reproduction of microorganisms in food, prevent food spoilage and prolong the shelf life of food, and are commonly used additives in food production. Preservatives are generally divided into acid preservatives, ester preservatives and biological preservatives. Commonly used are sodium benzoate, potassium sorbate, sulfur dioxide, lactic acid and so on. Used in condiments, jams, preserves, wine and other food processing.

Synthetic food additive food coloring is the same as other food additives, in order to achieve the purpose of safe use, strict toxicological evaluation is required.

①Chemical structure, physical and chemical properties, purity, form of existence in food, degradation process and degradation products.

② After the food is absorbed by the body, its retention distribution, metabolic transformation and excretion in tissues and organs.

③The biological changes caused by itself and its metabolites in the body, as well as the possible toxicity and mechanism of the body. Including acute toxicity, chronic toxicity, effects on fertility and reproduction, embryotoxicity, teratogenicity, mutagenicity, carcinogenicity, sensitization, etc.

Divided into two types of oxidizing bleaches and reducing bleaches. Oxidative bleaching agent is to oxidize and destroy the coloring substance through its own strong oxidation, so as to achieve the purpose of bleaching. Most reducing bleaching agents belong to sulfurous acid and its salts. These substances can produce sulfur dioxide, which will form sulfurous acid when it meets water. In addition to having a bleaching effect, it also has an antiseptic effect. In addition, due to the strong reduction of sulfurous acid, it can consume oxygen in fruit and vegetable tissues, inhibit the activity of oxidase, and prevent the oxidative destruction of vitamin C in fruits and vegetables.

Sulfites can be metabolized in the body to sulfates, which are excreted in the urine through the detoxification process. Compounds such as sulfites should not be used in foods of animal origin to avoid unpleasant odors. Sulfite has a destructive effect on vitamin B1, so foods with more B1 content such as meat, grains, dairy products and nuts are not suitable. Its use is strictly restricted in countries such as the United States because it can cause allergic reactions.